Air conditioning systems are currently commonplace in homes, office buildings and a variety of vehicles including, for example, automobiles. Over time, the refrigerant included in these systems becomes depleted and/or contaminated. As such, in order to maintain the overall efficiency and efficacy of an air conditioning system, the refrigerant in the system is periodically replaced or recharged.
Portable carts, also known as recover, recycle, recharge (“RRR”) refrigerant service carts, or air conditioning service (“ACS”) units, are used in connection with servicing refrigeration circuits, such as the air conditioning unit of a vehicle. The portable machines include hoses coupled to the refrigeration circuit to be serviced. In some current refrigeration systems the refrigerant, for example R134a or R1234yf, used is expensive and can be hazardous if released into the atmosphere. As such, a vacuum pump and compressor operate to recover refrigerant from the vehicle's air conditioning unit, flush the refrigerant, and subsequently store the recovered refrigerant in a refrigerant tank. The refrigerant can then be used in another refrigeration system. Recovering the refrigerant, however, requires the ACS unit to include filters, heat exchangers, a compressor, a storage tank, and a scale to weigh the storage tank.
Some newer air conditioning systems have begun using R744, or carbon dioxide, as an economical and eco-friendly refrigerant alternative. Removal of the R744 refrigerant from these air conditioning systems is done by venting the refrigerant to the atmosphere in a controlled manner. The R744, however, is at a very high static pressure in the air conditioning system at ambient conditions, such that the venting of the refrigerant must be controlled to prevent damage to components or elastomeric seals in the air conditioning system. What is needed, therefore, is an ACS unit that can accurately determine the flow rate of refrigerant vented from an air conditioning system during a service operation.
Additionally, it is advantageous to measure the total mass discharged from the air conditioning system to aid in diagnostics of the air conditioning system, for example to determine if the system has a leak. Since the R744 refrigerant is vented to atmosphere, and not captured, it is difficult or impossible in conventional ACS units to accurately determine the quantity of refrigerant removed from the air conditioning system during the venting. What is needed, therefore, is an ACS unit that can accurately determine total mass of R744 refrigerant vented from an air conditioning system during a service operation.